With the recent trend to higher-capacity information processing, various information recording technologies have been developed. Particularly, a surface recording density of an HDD using the magnetic recording technology has been continuously increased by a rate of approximately 100% a year. In recent years, an information recording capacity exceeding 250 GB per disk is required for a magnetic disk having a radius of 2.5 inch used in HDD or the like, and in order to meet such demand, realization of an information recording density exceeding 400 Gbits per 1 square inch is in demand. In order to achieve the high recording density in a magnetic disk used in an HDD or the like, magnetic crystal grains constituting a magnetic recording layer handling recording of an information signal need to be refined, and its layer thickness needs to be reduced at the same time. However, in the case of a magnetic disk of an in-plane magnetic recording method (also referred to as longitudinal magnetic recording method or horizontal magnetic recording method) having been merchandized, as the result of development of the refining of the magnetic crystal grains, thermal stability of the recording signal is damaged by a superparamagnetic phenomenon, and the recording signal is lost. A thermal fluctuation phenomenon begins to occur, which makes an obstructive factor to higher recording density of a magnetic disk.
In order to solve this obstructive factor, a magnetic recording medium of a perpendicular magnetic recording method has been proposed recently. In the case of the perpendicular magnetic recording system, different from the in-plane magnetic recording method, a magnetization easy axis of a magnetic recording layer is adjusted to be oriented in the perpendicular direction with respect to a substrate surface. As compared with the in-plane recording method, the perpendicular magnetic recording method can suppress the thermal fluctuation phenomenon, which is suitable for higher recording density. This type of perpendicular magnetic recording mediums include a so-called two-layer type perpendicular magnetic recording disk provided with a soft magnetic underlayer made of a soft magnetic body on a substrate and a perpendicular magnetic recording layer made of a hard magnetic body.
In a prior-art magnetic disk, a protective layer and a lubrication layer are provided on the magnetic recording layer formed on a substrate in order to ensure durability and reliability of the magnetic disk. Particularly, the lubrication layer used on the outermost surface requires various characteristics such as long-term stability, chemical substance resistance, friction resistance, heat resistant properties and the like.
In response to such request, a perfluoropolyether lubricant having a hydroxyl group in a molecule has been widely used as a lubricant for magnetic disk. For example, as in Japanese Patent Laid-Open No. S62-66417 (Patent Document 1), a magnetic recording medium on which a perfluoroalkylpolyether lubricant having a structure of HOCH2CF2O(C2F4O)p(CF2O)qCH2OH having a hydroxyl group at both ends of the molecule is applied is well known. If there is a hydroxyl group in a molecule of a lubricant, it is known that an adhesion characteristic to a protective layer of the lubricant can be obtained by an interaction of the protective layer and the hydroxyl group.